Aircraft landing aid system



Feb. 21, 1951 Filed llarch 30, 1946 H. w. cs. SALINGER 7 2,543,065

mcmm mums no SYSTEM 7 Sheets-Sheet 1 mvzmdn HANS wasnmsen ATTORNEY Feb. 27, 1951 H, w. s u 2,543,065

AIRCRAFT LANDING AID svs'rm Filed Batch 30, 1946 'T Sheets-Sheet 2 INVENTOR HANS W. G. SALINGER ATTORNEY 7 Sheets-Sheet 3 Filed March 30, 1946 a au e Ni; 5.53

m T R N E E G v m m L A S W NM 9 m A H $559.3 2&5 $556 muzmoum u zmrcamw p -54? $.53 52%: a z 3 5 0G 0N Feb. 27, 1951 H. w. G. SALINGER 2,543,065

AIRCRAFT LANDING AID. SYS

Filed March so, 1946 1 Sheets-Sheet 4 INVENTOR HANS W. G. SALINGER Feb. 27, 1951 H. w. G. SALINGER 2,543,065

AIRCRAFT LANDING AID SYSTEM Filed March 30, 1946 7 Sheets-Sheet 5 INVENTOR HANS W. G. SALINGER ATTORNEY Feb. 27, 1951 H. w. a. SALINGER AIRCRAFT LANDING AID SYSTm 7 Sheets-Sheet 6 Filed larch 3.0, 1946 Y mm m EN R VU O N T I & T 3 A W AU. 1 W s I .N I 8 3 A 1 1 L353 598 H @3235? v 2.5524 5235. 5.25225 Si ma? @5285 M52 2.5.3 5.5.3 2.585. 5522.525 a 0 a a 5 7 mm g mm 3 V E? 523% W: 5232 m n a a m. m. 225:3: r2513: w w u 2:523 2.2.23 2 we mm Feb. 27, 1951 H. w. a. SALiNGER AIRCRAFT mamas m SYSTEM Filed larch 30, 1946 7 Sheets-Sheet 7 r e tess-215 c!- amcam mimic am srs'reu mmasmmm-wmmosm, v mmtorsmmnnmn s nilcsuonmaimascra mcsa, 1;- "Im -1.1;

. I tofnavigational guide ,toweriseliminated. Whilestill'in the-air awaitjz isystemsfor' aircraftandn' ore particularlytosys ing his turn to land, the pilot of an aircr'ait is tems employingteievision principles for assistconcerned abouthisrelationship in space fing' ptsof dining conditions or low i fto the other aircraft still in the air. By provid- 1 v .8' ingeachpilotof anaircraftin'the vicinityofan -WhBnJe ndItiOnsoI such as airfield, -where in the ordinary course of opera- I at times 'whenffog'or low are tions there frequently arelarge numbers of airpresent or atnight time.- ithas 'ibeen" craft, with a view, preferably stereoscopic, of the in the past to guide aircraft towardpa landing space immediately over and surrounding an airfield by means such 'asradio which opfield showing therelationship of all of the airerateto transmit significant signals along; craft operating in the space. each pilot would be determined paths leading to. the j" j better fitted to properly, maneuver his aircraft to there have-been used radio-guid v "for avoid collisions with other aircraft. "In any such enabling a pilotto follow a path' 1 systems! course, greatly improvedresults may from an elevated position in space to a runway of 1 be obtained where facilities are provided to enthe airfield whereby the pilot may i'and' his V pable any pilot to identify his aircraft in the group crait'without' ever actually seeing the field. appearing in the stereoscopi'c view oithe space some of these latter-types of have. over an airfield. Not only willsuch a device enemployedtelevision principles to the pilotv able each pilot'to avoid collision with all other in making a landing. Generally, such 7 "aircraft, but also such afacility will have a scan the. airfield or at least a significant lpcrtion marked beneficial, psychological effect upon the thereof and transmit television signals to. the air: pilots... Byj'rernoving the feeling-that he is comcraft for use, in producing. on a viewing tube a. J "pletely-blind, each pilot will necessarily be rerepresentation of the' airfield. In som'elcasm. lievedof'a considerable nervous tension which is thr-ise television reproductions of the bound tobepresent when he feels that his visimade from previously taken photographs or the bilit'y is zero and he is completely reliant upon field. In any case. however, the information someone in a remote control point in order to I provided the-pilot of arr-aircraft by, such systems avoid collisions; ,Such a pilot will be better suited does not enable him to orient himselfv while still for the proper piloting of his aircraft than one in the air with respect to other aircraft which who is required to conduct such an operation may be operating in the vicinity ofthe airfield. under a high nervous strain.

In order to minimize the occurrence of colii- It, therefore, is an object of the present invensions between aircrait in the air over and around tion' to provide a system for depicting to a pilot an airfield, it is customary to require each airoi an, aircraft the objects such as other aircraft crait to circle the airfield; each at a difierent 5 present in the space over and around-a selected altitude. The pilots of the respective aircraft'rearea. 7 1 ceive; suitable instructions regarding the altitude Another object of the invention is to provide a at which they are to remain pending the receipt system for enabling an aircraft 'pilot to view of orders to land from a central control tower stereoscopically all objects in the space in-the located at the airfield. In general, the landing vicinity of a selected area. operations are controlled largely by means of Inaccordance with this invention there is proverbal instructions transmitted by radio to the vided an aircraft navigational aid system whereaircraft pilots from the control tower. It is dein the space over and around a selected area sirable to eliminate as much as possible of the such as an airfield is explored by radio transverbal communication between the control tower mitting and receiving means to determine the and the aircraft pilots. At a busy airport, it rerespective point in said space of all objects such quires one manvin a control tower to assume subas aircraft. The information derived is transstantially complete responsibility for all of the mitted by radio to each of the aircrafts which are aircraft operating in the vicinity of theairport. provided with facilities for producing optical ef- In many cases, particularly when visibility is fects which may be viewed by each of the respecpoor, the control tower cannot even see the airtive pilots.- In viewing these optical representacrait which it is required to control. tions of the objects in the space adiacent to the It is desirable to place as much responsibility airfield, each pilot is in effect able to view the as practical upon the pilots of the respective airspace as if he were standing on the ground at a craft, thereby lightening the burden upontheoppoint adjacen o he airfield and lookin int erator of the control tower. In this manner. the the space; possibility of accidents due to the failure or'short- More specifically in accordance with a preferred comings of the human element in the control embodiment of the invention, there is radiated 3 into the space to be explored, ultra-high frequency radiant energy which is pulsed substantially as in radar systems. This energy is reflected from each of the objects in the space to be explored. There also is provided at spaced points adjacent to the space two highly directive receivers of the reflected radiant energy. Each of these receivers is equipped with an antenna system whereby it is able to receive radiant energy from a relatively narrow solid angle. Each antenna system is provided with facilities for changing its direction so that it may systematically scan the entire space to be explored. The movements of the two receiver antenna systems are coordinated so as to scan the space synchronously. By reason of the spacing of the two receivers, the reflections from a given aircraft produce responses in the individual receivers at such 7 times in the respective scanning cycles to represent the point in space at which the aircraft is located relative to each of the receivers. Associated with the receivers is carrier wave transmitting apparatus by means of which the received reflection signals may b transmitted to receiving equi ment located in the aircraft. Each aircraft receiver includes indicating apparatus such as a cathode ray tube upon which light spots are produced in response to the received signals. The arrangement of corresponding spots of light on the indicating apparatus ordinarily will be different and will represent the relative positions of all of the aircraft operating in the explored space relative to the ground ultra-high frequency receiver which is in communication with the indicating apparatus. The pilot is provided with facilities for observing the indicating apparatus in such a manner that he receives a streoscopic view of the explored space and all of the objects located therein as if he were standing on the ground with one eye in the position of one of the ultra-high frequency radio receivers and the other eye in the position of the other high frequency receiver.

For a better understanding of the invention, together with other and further objects thereof, reference is made to the following description, taken in connection with the accompanying drawings, and its scope will be pointed out in the appended claims.

In the accompanying drawings:

Fig. 1 is a graphical representation of the space to be explored in accordance with the present invention and shows the relationship between the ultra-high frequency transmitting and receiving devices for making the desired exploration of the space;

Fig. 2 shows diagrammatically a complete communication system in accordance with the invention; I

Fig. 3 is a fragmentary view of the instrument panel of an aircraft employing facilities in accordance with one embodiment of this invention;

Fig. 4 is a schematic circuit diagram of one embodiment of the invention;

Fig. 5 is a diagrammatic detail of one of the ultra-high frequency radiant energy receivers;

Fig. 6 is an illustration of the simultaneous scansion of the space to be explored by the two spaced ultra-high frequency radiant energy receiving devices;

Fig. 7 is a view of two indicating devices located in the aircraft in accordance with one embodiment of the invention and depicting the relative positions of the indications representing '4 three objects located in the explored space somewhatasindicatedinliig. 1;

Fig. 8 is a schematic circuit diagram of another embodiment of the invention; and

Fig. 9 is a schematic circuit diagram of still another embodiment of the invention.

Having reference now to the drawings, attention will be directed first to Fig. 1. This figure shows an airfield I l and, in perspective, the space in the vicinity of the airfield. In the present embodiment of the invention, there is located outside of and at some distance from the airfield an ultra-high frequency transmitter l2. This transmitter which is not shown in detail may be entirely conventional and of the type used generally for many purposes in radar systems. For the present purpose, it will be assumed that the transmitter is provided with directive equipment for radiating pulsed ultra-high frequency radiant energy into the space designated generally by the'three-dimensional figure H of which one of the sides is in the ground plane. It will be apparent after a more detailed description of the illustrative embodiments of the invention that other means may be employed for radiating ultrahigh frequency radiant energy throughout the entire space to be explored. For example, the transmitter may be located on the airfield so as to radiate the ultra-high frequency radiant energy'throughout a hemispherical space over and around the airfield.

The high frequency radiant energy is intercepted by any objects such as the three airplanes IS, IS and I! located within the space to be explored. Two receivers l8 and 19 are located in spaced relationship to one another at a point outside of the airfield. These receivers are equipped respectively with directive antenna systems illustrated diagrammatically herein by the horns 2i and 22. Each of these receiver antenna systems is designed to receive any reflected ultrahigh frequency radiant energy from a relatively small-portion of the space to be explored. This characteristic of the receivers is illustrated in Fig. 1 wherein the section 23 is representative of an incremental section of the total space to be explored. The horns II and 22 of the high frequencyreceivers are each provided with facilities for so directing the horns that the entire space may be explored systematically according to a fixed scanning pattern. The receiver horns are controlled to operate synchronously so that at any instant they are both directed toward the same elemental area of the most remote vertical plane bounding the space to be explored.

Referring now to Fig. 2 of the drawings, a complete communication system between the ground apparatus and each of the aircraft such as the plane Ii operating in the space being explored is shown diagrammatically. One of the rays 24 of ultra-high frequency radiant energy emanating from the transmitter 12 is shown impinging upon the plane [6. One of the reflected rays 25 is received by the ground receiver l8 and another one of the reflected rays 26 is received by the ground receiver IS. The reception of the reflected rays 25 and 26 by the respective receivers l8 and I! does not occur necessarily simultaneously as will be apparent from a more detailed description of the system to follow.

A carrier wave transmitter 21 is associated with the ground receiver l8 and another carrier wave transmitter 28 is associated with the ground receiver IS. The transmitters Hand 28 radiate carrier waves such as represented at 29 and 3|,

respectively, which are modulated with the information received by the associated respective ground receivers I3 and I3. The carrier wave energy 23 and 3| is intercepted respectively by antennas 32 and 33 located on the plane it. The information conveyed to the aircraft in this manner is utilized to produce the desired visual effects in the airplane for observation by its pilot in a manner to be described subsequently.

In order to clearly describe the underlying principles of the invention, the instant illustrative embodiment includes two carrier wave transmitters 21 and 28. It will be understood that the invention may be practiced without employing this particular arrangement. As disclosed in additional embodiments of the invention to be described, other communication facilities may be invention. For example, a single relatively low frequency transmitter may be employed to relay the signals from the ground station to the airplanes. Such a transmitter will be capable of radiating a single carrier wave which may be modulated in a, conventional manner .to provide two distinct char communication. One way of accomplishti ."1 a result is to modulate the single radiatedv rier wave by two sub-carrier waves of different frequencies, each subcarrier wave in turn being modulated with the intelligence signals. In such a case the receiving equipment located in the airplanes will be provided with facilities for selectively receiving the two sub-carrier waves.

In the airplane there are provided two radiant energy receivers 34 and 35 connected respectively to the antennas 32 and 33. A cathode ray tube 36 having a viewing screen 31 is electrically connected to the carrier receiver 34 and the tube is mounted so that the viewing screen thereof occupies a left-hand position in the instrument panel 38 of the airplane. Similarly, a cathode ray tube 39 is connected to the carrier receiver 35 and has its viewing screen 43 mounted in the instrument panel to the right of the viewing screen 31. In addition there is mounted on a bracket 4| or other suitable structure a stereoscoplc viewing apparatus including a pair of lenticular devices 52 and 63 to enable the pilot to view simultaneously the two screens 31 and 33 stereoscopically.

Referring now to Fig. 4 of the drawings, there is shown a schematic circuit diagram of the form of invention illustrated in Figs. 2 and 3. The two directive horns 2| and 22 are controlled respectively by scanning mechanisms 44 and 45. A typical mechanism for controlling the directive movements of the horns will be described subsequently. For the present, it will be understood that the scanning mechanisms are capable of moving the associated horns to follow a predetermined scanning pattern, whereby the complete space may be explored in a succession of elemental sections. Any reflected high frequency radiant energy received by the horn 2| in its directed movements is impressed upon the associated antenna which is connected to the ground receiver iii. The output of this receiver is coupled to the carrier transmitter 21 to modulate the radiated carrier wave in accordance with the intelligence received by the horn 2|. This carrier wave in turn is impressed upon the carrier receiver 34 located in the aircraft and is eflec- 8 tive to suitably modulate the intensity of the electron beam in the cathode ray tube 38.-

Similarly, the high frequency reflected energy received by the horn 22 is impressed upon the ground receiver IS, the output circuit of which is coupled to the carrier transmitter 23 for the purpose of modulating the radiated; carrier wave by.

' the scanning movements of the'horns 2t and 22 and the deflections of the electron beams in the respective cathode ray tubes 33 and '33. For this purpose there is provided a synchronizer 43 which may be a conventional timing unit used generally in television systems for a similar purpose. The synchronizer is coupled to the driving apparatus for the two scanning mechanisms 33 and 45. By

this means, the two scanning mechanisms are so coordinated that the associated horns 2| and 22 are synchronously moved to scan the space to be explored simultaneously. The synchronizer also is coupled to the two carrier transmitters 21 and 23 for the purpose of introducing synchronizing signals for modulation upon the respective radiated carrier waves. As in conventional television systems, these synchronizing signals may comprise a first series of signals occurring at,;

the line frequency of the scanning movements of the two directive horns and a second series of signals occurring at the frame frequency. The line and frame synchronizing impulses preferably-will be mixed with the intelligence signals so as to occur during retrace periods of the scanning mechanisms. It will be understood that the receiving equipment located in the aircraft will include conventional circuits for separating the synchronizing signals from the intelligence signals and for suitably impressing the synchronizing signals upon the deflection circuits (not shown) with which each of the cathode ray tubes 35 and 39 is provided. In this manner, the desired synchronism between the electron beam deflections and the scanning movements of the horns 2| and 22 may be maintained.

Having reference now to Fig. 5 0f the drawings, there is illustrated schematically the directive antenna equipment with which each of the ultrahigh frequency ground receivers may be provided. The antenna systems of both receivers may be identical and hence only one will be described in detail herein. The receiver i8 is connected by means of a pair of flexible conductors 31 and 33 to a dipole antenna. 49 mounted in the directive horn 2|. Preferably, the connecting conductors will be a coaxial cable. The antenna is so located in the horn and the horn itself is so designed that the antenna is responsive only to the energy received from a relatively small solid angle extending out into the space to be explored. Preferably, this angle should be 5 degrees or less. The horn ii is mounted at the end of an arm 53 which is supported on a pivot 3| rigidly attached to a platform 52. The arm 50 is adapted to rotate on the pivot Si in a plane parallel to the plane of the platformfl. A retractile spring 53 is attached at one end to the rearwardly extending portion of the arm 33 and at the other end to means such as a pin 54 secured to the platentire time of one revolution of the shaft 1 I.

form 52. The spring 53 so biases the arm 56 that normally it rests against a stop pin 55 secured to the platform.

The platform itself is pivotally mounted on a pair of brackets 56 and 51 which are secured to a base plate 58. Another retractile spring 59 is attached at one end to the underside of the platform 52 and at the other end to the base plate 58 so that normally the platform is urged into engagement with a stop pin 60 secured to the base plate.

The rearwardly extending portion of the arm 56 is provided with a depending portion 6| which extends through an opening 62 formed in the base plate. This opening is arcuate to conform to the path of the depending portion as it moves about the pivot The outer edge of the depending portion 6| also is curved substantially as illustrated to conform to the tilting of the platform 52.

The apparatus also includes a sub-base plate 63 attached by any suitable means such as a plurality of brackets 64 to the base plate 58. A

motor 65 is mounted on the sub-base plate which during the time of one revolution of the shaft 61. The configuration of the cam also is such that at the end of each revolution thereof, the depending portion 6| momentarily is disengaged permitting the retractile spring 53 to return the arm to its original starting position substantially instantaneously. The described movements of the arm 56 efiected by the cam 68 and associated apparatus produces a movement of the horn 2| relatively slowly from left to right as viewed in the drawing followed by a quick restoration of the horn to its original starting point.

A worm gear 69 also is attached to the shaft 61. An auxiliary shaft 1| suitably journaled in brackets 12 and 13 which are attached to the base plate 58 is provided with a pinion gear 14 at its rear end. The pinion gear meshes with the worm gear 69 so that the shaft 1| is driven in the direction of the arrow. A relatively low speed cam is attached to the forward end of the shaft 1| in position to engage the underside of the rear portion of the platform 52. The cam 15 is so shaped to tilt the platform 52 at a relatively slow uniform rate during substantially the Additionally the configuration of the cam 15 is such to disengage the platform 52 after it has been tilted to one extreme position and to permit the retractile spring 59 to quickly return the platform to its original starting position against the stop pin 60. The tilting movements of the platform 52 effect a. gradual downward movement of the horn 2| to an extreme position and a quick restoration of the horn to its original starting position.

The gear ratio between the worm 69 and the pinion 14 is chosen so as to provide the desired relationship between the scanning movements of the horn 2|. In a particular illustrative case, it will be assumed that the area to be scanned or explored comprises a total of 81 elemental sections arranged in 9 rows of 9 sections each. In

such a case the gear ratio will be such that the shaft 61 is required to make 9 complete revolutions for each complete revolution of the shaft 1|. It will be seen that the path traced by the horn 2i will proceed back and forth through the space to be explored and at the same time gradually downward through the space until the lower right hand elemental section of the space is explored. after which it is quickly restored to its original starting position in the upper left hand section of the space.

As previously stated, both of the ultra-hi h frequency receivers I8 and I9 are similar. The mechanism associated with the receiver I9 for effecting scanning movements of its horn 22 may be identical to that described for the receiver I8. The mechanism may be driven by a motor similar to the motor 65. In order to effect sy chronous movements of the two receiver horns, the two driving motors may be of the synchronous type and may be energized from the same alternating current source. Obviously other conventional apparatus such as that indicated in Fig. 4 may be employed alternatively to effect the synchronous movements of the two horns.

For the purpose of describing the operation of the apparatus embodying the invention, it will be assumed that there are three objects such as the airplanes I5, l6 and I1 of Fig. l in the space to be explored. It also will be assumed that these airplanes are operating at such altitudes that the airplane I5 will be scanned by the receiving apparatus during the first horizontal movement of the horns 2I and 22. Similarly the airplanes I6 and I1 are assumed to be flying at such high altitudes that they will be scanned on the second and third horizontal movements respectively of the receiver horns 2| and 22.

In order to illustrate the operation of the apparatus, a projection in the horizontal plane of the airfield is made of the space to be explored as illustrated in Fig. 6. The quadrilateral 16 represents the horizontal projection of the space to be explored. For ease in distinguishing the three airplanes, they are represented in this figure by a rectangle I5, a triangle I6 and a circle I1 corresponding respectively to the airplanes I5, I6 and I1 of Fig. 1. At the start of a scanning movement by the two receivers I 8 and I9, the directive antenna apparatus is pointed toward the upper left hand corner of the quadrilateral 16. During the scanning movement of the two directive antenna equipments, the angular relationship of each changes uniformly with respect to time. In

' this figure, the directions of the antenna associated with the receiver I8 is indicated by the broken lines while the directions of the antenna apparatus associated with the receiver I9 are shown by the solid lines extending from the respective receivers.

The following portion of the description is taken in conjunction particularly with Figs. 6 and '1. The electron beams of the cathode ray tubes 36 and 39 are deflected over their respective screens 31 and 40 in synchronism with the movements of the receiver horns 2I and 22. synchronism may be maintained in a conventional manner as described over the carrier wave communication channels between the ground transmitters 21 and 28 and the airplane receivers 34 and 35. As the two antenna systems are moved, the receiver I9 first receives a series of reflected ultra-high frequency pulses from the object I5. At this time the horizontal angle through which the antenna system of the receiver I8 is moved from its starting point is not great enough to bring it into position to receive radiant energy from the object I; therefore, the carrier wave transmitter associated with the receiver l9 sends a signal to all of the airplanes which is translated in the respective airplanes into a spot of light 11 on the screen of the right hand cathode ray tube screen 40. A short time later when the antenna of the receiver I! has been rotated out of its position for receiving energy from the object IS, the antenna of the receiver I8 is in position to receive reflected energy from the object i5. Thus the carrier wave transmitter associated with this receiver sends a signal to the airplanes which is converted ject l6 which results in the production of a spot.

of light 19 on the right hand tube screen 40. A short time thereafter, the receiver i8 receives reflected energy from the object I 6' and there is produced a spot of light 8| on the left hand tube screen 37.

The interception of reflected energy from the object ll by the receivers it and I 9 during their third elemental scansion of the space produces first a spot of light 82 on the screen 48 and then a spot of light 83 on the screen 31. It

will be noted that the light spots Ti; 19 and 82 are closer to the left hand edge of the screen at than the corresponding light spots 18, Bi and 83 are to the left hand edge of the screen 31. This is the same eifect that would be produced invidiually in the right and left eyes respectively of an observer located in the position of the two ground receivers I8 and IS. The closer the object is to an observer, the greater is the apparent shift in space as viewed first by one eye and then by the other. Thus, the relatively large displacement of the light spots 82 and 83 indicates that the airplane I1 is the closest of the three objects to the receivers l8 and I9.

When these two screens are viewed by the pilot by means of the stereoscopic facilities provided as indicated in Fig. 3, the screen 31 is seen only by his left eye and the screen 40 only by' his right eye. Additionally, the two screens are in effect optically superimposed in a well known manner so as to create the same impression upon the pilot as if he were standing on the ground with his two eyes respectively in'the positions of the receivers ment in forms other than that previously de-' scribed. In Fig. 8 there'is illustrated schematically a circuit arrangement in accordance with another embodiment of the present invention. The directiveantenna horns 2! marine moved by the associated scanning mechanisms 44 and 45 to provide the high frequency ground receivers i8 and H with the intelligence concerning the 7 locations of objects within the explored space as in the previously described embodiment of the invention. In this case, however, a single carrier wave transmitter 84 is, employed to relay the intelli'gence to the aircraft. The output circuits of each of the high frequency receivers l8 and I8 are coupled to switching apparatus 85. Such apparatus may be entirely conventional but preferably it is in the form of an electronically operated 5 switch. The output circuit of the switching apparatus is coupled to the carrier transmitter 84. The switching apparatus functions to alternately connect the output circuits of the receivers l8 and I9 to the input circuit of the transmitter 84. The synchronizing unit 46 is coupled to the scanning mechanisms 44 and 45 as in the previously described embodiment of the invention to control these mechanisms in the desired manner. The synchronizer also is coupled to the carrier transmitter 84 as in the previous instance to interject synchronizing signal impulses into the intelligence signals modulated on the carrier wave. Also the synchronizer is coupled to the switching apparatus 85 to control its operation.

The airplane is provided with a single carrier wave receiver 86 which is designed to be responsive to the carrier wave radiated by the transmitter B4. The intelligence signals and the system control signals such as the synchronizing impulses are separated by the receiver in a conventional manner and the intelligence signals are impressed upon the input circuit of a switching apparatus 81. This apparatus is provided with two output circuits which are coupled respectively to the control circuits of the cathode ray tubes 36 and 39. The switching apparatus may be conventional and similar to the ground switching apparatus 85. It functions to connect the output circuit of the carrier receiver 86 alternately to the control circuits of the respective cathode ray tubes 36 and 39. The synchronizing impulses derived from the receiver 86 are impressed by means of a suitable coupling upon a synchronous power source 88. This power source is connected to the switching apparatus 81 in a manner to control its operation.

In operation, the scanning mechanisms 43 and 55 function to direct the antenna horns 2| and 22 respectively in a manner to explore the space in the vicinityof the airfield, whereby to impress intelligence signals representative of the location of objects in the space upon the respective receivers I 8 and I!) as in the previously described embodiment of the invention. Both of the an- Qjtenna hor ns' are continuously scanning the space that ,both of the receivers I8 and iii are continuously responsive to the received ultra-high frequency reflections. The switching apparatus BS functions, however, to couple first the output circuit of the receiver ill to the carrier transmitter 84 for a predetermined time such as the a period of one frame or complete scansion of the space. During this time the carrier wave which is transmitted to the airplane receiver 86 is modullatedby the intelligence received by the receiver Also during this time the switching apparatus BIon the airplane is operatiye to couple the output circuit of the aircraft receiver 86 to the cathode ray tube 36. In this manner the intellicence received by the high frequency ground receiver I0 is indicated upon the screen or the cathod ray tube 36. During the next frame 0 period the switching apparatus 85 couples the output circuit of the ground receiver l9 to the carrier transmitter 84 and the airborne switching apparatus 81 couples the output circuit of the carrier receiver 85 to the cathode ray tube 38. Thus, the intelligence received during this period by the ground receiver I8 is indicated on the viewing screen of the cathode ray tube 88.

The screens of the tubes 88 and 88 are viewed as before through a stereoscopic device including the lenses l2 and 43. The pilot, thus, is able to obtain substantially the same stereoscopic indication as in the previous instance. With respect to the cathode ray tubes 88 and 39, the only difference in their operations is that in the first case the two indications are impressed upon the respective viewing screens concurrently, while in the case of the embodiment under discussion, the two indications are impressed upon the viewing screens in alternation. By the use of cathode ray .tubes having fluorescent screens with sufficiently long persistence and/or by operating the system so as to increase the scanning frequency of the space to be explored, the optical eifect obtained by the pilot viewing the two tubes will be substantially the same as in the first case.

Referring now to Fig. 9 of the drawings, there is illustrated schematically still another embodiment of the invention. In this form, the ground receiving and retransmitting apparatus is substantially identical with the apparatus shown in Fig. 8. The airplane is provided with a single carrier receiver 86 of which the output circuit for the intelligence signals is coupled to a cathode ray tube 88. A disc 8| having a plurality of segments, of which there are at least two, is mounted on a shaft 82 and arranged so that the disc segments may be rotated in front of the viewing screen of the cathode ray tube 88 much in the same manner as a color filter disc is employed in some color television systems. The disc consists of segments of two different types, both of which are light polarizing devices such as Nicol prisms or the like. One of the polarizing segments 98 is of a character to polarize the light transmitted thereby horizontally, while the other polarizing segment 94 is adapted to polarize the light vertically. The shaft 92 is driven by any suitable means such as that indicated by the motor 95.;The power or at least a controlling component thereof for energizing motor 85 is derivedfrom a synchronous power source 88 which is coupled to the receiver 88 in a manner to receive the synchronizing signal impulses. Additionally, there is provided for use in conjunction with the cathode ray tube and the light polarizing disc, a viewing device such as a pair of spectacles or goggles 96. The spectacles may be worn by the pilot or they may be attached to the apparatus in any conventional manner such as by making them part of alight shielding hood, for example. The spectacles are provided with a horizontally polarized unit 91 for the right eye and a vertically polarized unit 88 for the left eye.

In operation, the intelligence received by the ground receivers i8 and i8 is alternatively transmitted from the carrier transmitter 84 to the airborne carrier receiver 86. While this information is being portrayed on the viewing screen of the cathode ray tube 89, the vertical polarizing segment 94 is passing between the screen and the observers viewing device 96. Consequently the vertically polarized light is transmitted only by the vertically polarized unit 98 to the left eye of the observer. The screen is effectively obscured from the right eye by means of horizontally polarized unit 91. During the succeeding frame interval, while the high frequency ground receiver I9 is coupled by the switching apparatus 85 to modulate transmitter 88, the horizontal light polarizing segment 88 is rotating in front of the screen of the cathode ray tube 88. In this case the light is permitted to pass through the horizontally polarized unit 81 to the right eye of the observer and is prevented from reaching the left eye by the vertically polarized unit 88.

While there have been described several illustrative embodiments of the invention, it will be obvious to'those skilled in the art that various changes and modifications may be made therein without departing from the invention, and it, therefore, is aimed in the appended claims to cover all such changes and modifications as fall within the true spirit and scope of the invention.

What is claimed is:

1. An aircraft navigation system comprising means for radiating ultra-high frequency radiant energy throughout a predetermined space in the vicinity of a selected area, a pair of ultra-high frequency radiant energy receivers located at spaced points, means for causing said receivers to scan said predetermined space whereby to receive two respective series of reflections of said radiant energy from objects located in said space, means for transmitting signals representative of said two series of received reflections, indicating apparatus in one of said objects responsive to said transmitted signals for producing indications of all of the objects in said space, and means for viewing said indicating apparatus to obtain a stereoscopic representation of all of the objects in said space.

2. An aircraft navigation system in accordance with claim 1 wherein said signal transmitting means comprises a single carrier wave transmitter, and means for alternately coupling each of said receivers to said carrier transmitter.

3. An aircraft navigation system in accordance with claim 1 wherein said signal transmitting means comprises a single carrier wave transmitter, and said indicating apparatus includes means for alternately producing indications of the intelligence received by said two receivers, and means for alternately coupling said receivers to said carrier transmitter.

4. An aircraft navigation system in accordance with claim 1 wherein said signal transmitting means comprises a carrier wave transmitter, and said indicating apparatus includes a pair of cathode ray tubes, switching apparatus for connecting said two receivers in alternation to said carrier transmitter, and means including switching apparatus in said object for rendering said cathode ray tubes responsive to said transmitted signals in alternation.

5. An aircraft navigation system in accordance with claim 1 wherein said signal transmitting means comprises a single carrier wave transmitter, said indicating apparatus includes a single cathode ray tube, and said viewing means for the tube including means for rendering the tube screen visible alternately to the left and right eyes of an observer, means including switching apparatus for coupling said two receivers to said carrier wave transmitter in alternation, and means for rendering said tube responsive to said transmitted signals.

6. An aircraft navigation system comprising, means for radiating ultra-high frequency radiant energy throughout a predetermined space over and adjacent to a selected area, a pair of radiant energy receiving devices located at spaced points, means for causing said receivers to scan said predetermined space in elemental sections whereby to receive reflections of said ultra-high frequency radiant energy from aircrafts located in said space, means for retransmitting signals representative of said received reflections, means in each of said aircraft including a pair of indicating devices responsive to retransmitted signals from said respective receiving devices to produce indications in relatively the same positions as the aircraft are located in the scanning pattern of the corresponding ground receiving device, and means for stereoscopically viewing said indicating devices simultaneously to obtain a stereoscopic representation of all of the aircraft operating in said predetermined space.

7. An aircraft navigation system comprising, means for transmitting ultra-high frequency radiant energy throughout a predetermined space over and adjacent to an airfield, a pair of radiant energy receiving devices located at spaced points, each of said receivers having mechanism for scanning said predetermined space in elemental sections whereby to receive reflections of said ultra-high frequency radiant energy from aircraft located in said space, retransmitting apparatus associated with said receivers and responsive to received reflections, said retrans- -mitting apparatus being adapted to provide two carrier wave communication channels modulated by the respective received reflections, receiving apparatus located in each of the aircraft operating in said predetermined space and responsive respectively to said two carrier wave channels, two cathode ray tubes included in each of said aircraft receiving apparatus, each of said cathode ray tubes being adapted to delineate a light spot on its viewing screen in response to each received impulse from said respective carrier wave channels whereby to produce light spots on the respective viewing screens in relatively the same positions as the aircraft from which the corresponding reflections are received are located in the scanning pattern of the corresponding ground receiving apparatus, and a stereoscopic device for viewing the screens of said cathode ray tubes simultaneously to obtain a stereoscopic representation of all of the aircraft operating in said predetermined space.

8. An'aircraft navigation system comprising, a transmitter for transmitting ultra-high frequency radiant energy throughout a predetermined space over and adjacent to said airfield, a pair of radiant energy receiving devices located at spaced points outside of said airfield and each having a relatively narrow angle antenna system directed into said predetermined space, each of said receivers having mechanism for synchronously moving said directive antenna systems to systematically scan said predetermined space .whereby to receive reflections of said ultra-high of said cathode ray tubes being adapted to delineate a light spot on its viewing screen in ciated retransmitters whereby to produce light spots on the respective viewing screens in relatively the same positions as the aircraft from which the corresponding reflections are received are located in the scanning pattern of the corres onding ground receiving apparatus, and a stereoscopic device for viewing the screens of said cathode ray tubes simultaneously to obtain a stereoscopic representation of all of theaircraft operating in said predetermined space.

9. An aircraft navigation system comprising, a transmitter located outside of an airfield and having relatively wide angle radiant energy directive apparatus for transmitting ultra-high frequency radiant energy throughout a predetermined space over and adjacent to said airfield, a pair of radiant energy receiving devices located at spaced points outside of said airfield and each having relatively narrow angle antenna apparatus directed into said predetermined space, each of said receivers having mechanism for synchroncusly moving said directive antenna apparatus on a fixed pattern to systematically scan said predetermined space in a succession of elemental sections radiating respectively from said receivers whereby to receive reflections of said ultra-high frequency radiant energy from aircrafts located in the particular elemental sections being scanned, retransmitting devices associated with said respective receivers and responsive to received reflections, each of said retransmitting devi;es being adapted to radiate a distinctive relatively low frequency carrier wave modulated in amplitude by the respective received reflections, a pair of receiving devices located in each of the aircraft operating in said predetermined space and responsive respectively to said two low frequency carrier waves, a cathode ray tube included in each of said aircraft receiving devices mounted with the viewing screens thereof adjacent to one another in substantially the same plane, each of said cathode ray tubes being adapted to delineate a light spot on its viewing screen in response to each received impulse from said associated retransmitting device, means for synchronizing the deflecting movements of said ground directive antenna apparatus and the electron beams of the respective cathode ray tubes whereby to produce light spots on the respective viewing screens in reiativelythe same positions as the aircraft from which the corresponding reflections are received are located in the scannin (ill response to each received impulse from said assopattern of the corresponding ground receiving apparatus, and a stereoscopic device for viewing the screens of said cathode ray tubes simultaneously to obtain a stereoscopic representation of all of the aircraft operating in said predetermined space.

HANS W. G. SALINGER.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 2,132,599 Baumann Oct. 11, 1938 2,321,698 Nolde June 15, 1943 2,358,646 Klemperer Sept. 19, 1944 2,388,170 McCollum Oct. 30, 1945 2,408,050 De Rosa Sept. 24, 1946 2,416,155 Chubb Feb. 18, 1947 2,417,446 Reynolds Mar. 18, 1947 2,455,456 Wittaker Dec. 7, 1948 

